Medical, in particular dento-medical, powered instruments often require that the operating state should be continuously monitored to control or adjust the output of an electric drive or of another electric component on the basis of these measurements, for example. This is very important in medical instruments such as a powered scaling hand-piece (scaler hand-piece), as these instruments comprise, for example, an electric vibration generator (e. g. a piezoelectric motor). In the ideal case, the piezoelectric motor (vibration generator with piezoelectric elements) operates at a resonance frequency which is to be provided by the applied electric signal for an optimum operation. In this case, the problem occurs that the resonance frequency depends, for example, on the load and may therefore continuously change during use.
Patent specification U.S. Pat. No. 6,976,843 B2 discloses a dental treatment device allowing a plurality of hand-pieces operating at different resonance frequencies to be operated by means of an ultrasonic generator. The adjustment to the resonance frequencies is done through passive elements such as capacitors, which, together with the hand-piece, are connected to the ultrasonic generator. The passive elements have the effect that the resonance frequency provided by the ultrasonic generator for the respective hand-piece is appropriately adapted to the hand-piece.
Patent specification No. EP 1 191 895 B1 discloses a control device for a dental ultrasonic hand-piece, which is configured to electrically compensate for a phase shift occurring between the voltage and the supplied current due to an intrinsic capacitance of the ultrasonic generator. To that end, a secondary circuit is arranged in addition to the primary circuit, which is connected to the primary circuit through a converter and comprises a variable inductance and a variable capacitance on the secondary side. If the hand-piece does not operate at the resonance frequency due to loading, for example, and the current and voltage signals exhibit a relative phase shift, the inductance is changed on the secondary side of the converter so that the phase of the current on the primary side will also shift and in turn the hand-piece is allowed to be brought into resonance.
The patent specification mentioned first only allows an adjustment of the resonance frequency by means of one or more passive elements and hence only an adjustment to discrete resonance frequencies is possible, whereas the second patent specification utilizes a secondary circuit in order to first sense a measurand such as a relative phase shift between the current signal and the voltage signal and then to compensate for the determined phase shift by means of continuously changing the inductance on the secondary side.
The disadvantage of these two approaches is that it is impossible to detect the operating state in a flexible and low-loss manner and to make an adjustment on the basis of this detection, which continuously allows a resonant operation. Another disadvantage is that the control is accompanied with losses due to additional inductances/capacitances, which are not acceptable for many applications.
Therefore, an improved medical treatment device and an improved control of the medical treatment device are demanded, which in particular allows to continuously detect and control the operating state of the treatment device through simplest possible means and at the lowest possible loss.